The present invention relates to a reaction and distillation device and to a process for preparing a tertiary alkyl ether by reaction of at least one olefin with an aliphatic monoalcohol, generally in excess.
It is well-known to prepare tertiary alkyl ethers by reacting an iso-olefin generally contained in a hydrocarbon fraction with an aliphatic alcohol, generally used in excess, in the presence of an acid catalyst, for example sulfuric acid, hydrofluoric acid, aluminium chloride or boron fluoride, or in the presence of carbonaceous matter containing sulfonic groups (xe2x88x92SO3H), for example sulfonated coal, sulfonated phenol-formaldehyde resins, sulfonated coumarone-indene polymers or preferably sulfonated styrene-divinylbenzene copolymer resins or other compounds, notably mineral compounds, comprising sulfonic groups (for example sulfonated polysiloxanes).
It has been known for a long time that the reaction between an aliphatic monoalcohol and a tertiary olefin is balanced and that it is difficult to obtain iso-olefin conversion coefficients with a high purity and yield. Conventional processes such as those described for example in Hydrocarbon Technology International, Autumn 95, p. 21-27, comprise one or more reactor(s) for etherification to tertiary alkyl ethers followed by at least one fractionating zone, generally a distillation zone, whose bottom product is ether containing the lowest possible amount of monoalcohol(s).
This is the reason why the prior art recommended, in order to improve the performances of this synthesis, to add a complementary reaction section to the main reactor, as described for example in patent U.S. Pat. No. 5,364,975 in the name of the applicant. In this patent, the complementary reaction section is included, according to a preferred embodiment, in the reflux device of the fractionating section. It has also been proposed, for example in patent U.S. Pat. No. 4,503,265 or in patent applications WO-A-93/19,031 and WO-A-93/19,032, to draw off a product from an intermediate tray of the fractionating section, to feed this product into a complementary reaction section and to feed the product from this complementary reaction section back into the fractionating section at a level below the draw-off level. The drawback of this embodiment is that it disrupts the smooth running of the distillation process in the fractionating section. A process of the UOP Company known as Ethermax, wherein the effluent from the main etherification section is fed into a distillation-reaction zone, has also been described for example in Hydrocarbon Processing, March 1995, p. 114. As shown hereafter in a comparative example, this process has the drawback of requiring a column of very great height to obtain a very appreciable improvement of the global performances. These conventional processes for preparing tertiary alkyl ethers will be described hereafter in connection with FIGS. 1, 2 and 3.
One of the objects of the invention is to overcome the main drawbacks of the processes described in the prior art and to propose several ether synthesis embodiments allowing to maximize global conversion of the iso-olefins contained in hydrocarbon cuts.
The feed consisting of a mixture of C4, C5, C6 or C7 hydrocarbons comprising iso-olefins and at least one aliphatic monoalcohol generally used in excess is fed into the main reaction section represented by reactor R1 in FIGS. 1 to 9. The mixed reactants are brought into contact with an acid catalyst.
The product from this reaction section R1 is fed into a distillation zone represented by column F1 in FIGS. 1 and 2 and by column F2 in FIG. 3. It is distilled in this column in order to produce, at the bottom, through line 9, a tertiary alkyl ether containing the lowest possible amount of monoalcohol(s), and at the top, through line 2, a mixture of reactive and non reactive hydrocarbons and of aliphatic monoalcohol(s) carried over by azeotropy. This effluent flowing out through line 2 is condensed in condenser E1 and collected through line 3 in drum B1 prior to flowing into pump P1 through line 4.
In the instance schematized in FIG. 1 patent U.S. Pat. No. 5,364,975), part of the effluent leaving pump P1 is fed through line 10 into a reactor R2 referred to as finishing reactor, whose effluent is fed through line 12 into column F1 as reflux and the rest of the effluent flows off as distillate through line 6.
In the embodiment schematized in FIG. 2 (patent U.S. Pat. No. 4,503,265), a product is drawn off from an intermediate tray of the distillation column between the effluent introduction point of etherification reactor R1 and the top of this column, and this product is fed through line 10 into a reactor R2 referred to as finishing reactor, whose effluent is fed through line 12 into column F1 at a level below the level of the draw-off point. In the instance schematized in FIG. 2, part of the effluent flowing out of pump P1 is fed through line 5 into column F1 as reflux and the rest of the effluent flows off as distillate through line 6.
In the embodiment schematized in FIG. 3 (Hydrocarbon Processing, March 1995, p.114), the effluent of the reaction section R1 is fed into a distillation-reaction column beneath the first catalyst bed and part of the effluent flowing out of pump P1 is fed through line 5 into column F2 as reflux and the rest of the effluent flows off as distillate through line 6.
However, such a process requires in the instance schematized in FIG. 3 a great number of reaction zones in distillation-reaction column F2 in order to obtain high conversions into iso-olefins and consequently a column of great height. In fact, obtaining high conversions requires a distillation-reaction column containing many reaction zones. Insofar as one of these zones alone occupies about 3 meters in height in the distillation-reaction column, the final height of this column quickly becomes limitative. It would therefore be interesting to have such a high conversion to iso-olefins while keeping a limited number of reaction zones in the column and/or to limit the height of the column. This is one of the objectives of the invention as described hereafter in connection with FIGS. 4, 5, 6, 7, 8 and 9.
The present invention thus relates to a distillation and reaction device comprising:
a) a reaction section,
b) a distillation-reaction section comprising a distillation zone, comprising at least one means intended for circulation of the effluent from the reaction section to said distillation zone, and at least one distillation-reaction zone, comprising at least one catalyst bed, said distillation-reaction zone being distinct from the distillation zone and providing at least partly, preferably for the most part most preferably practically entirely the reflux of the distillation zone.
The device according to the invention preferably comprises at least one means intended for circulation of the effluent between the top of the distillation zone and the bottom of the distillation-reaction zone and at least one means intended for circulation of the effluent between the bottom of the distillation-reaction zone and the top of the distillation zone.
The device according to the invention preferably also comprises at least one means for feeding the reaction section and at least one means for drawing off product at the bottom of the distillation zone.
According to one of the embodiments of the invention, independent or not of the previous embodiments, the device according to the invention is such that the distillation-reaction zone comprises at least one reflux device, which generally comprises at least one draw-off means situated at the top of the distillation-reaction zone, feeding at least one condensation zone, at least one means intended for circulation of part of the effluent from said condensation zone towards the top of the distillation-reaction zone and at least one means for drawing off (generally outside the distillation-reaction section) another part of the effluent from the condensation zone.
A preferred implementation of the device according to the invention is preferably such that said device is characterized in that said distillation-reaction section comprises at least one complementary reaction section, comprising at least one catalyst bed. Such a preferred implementation comprises three embodiments which are described hereafter, and said embodiments can be combined with one another for said preferred implementation of the device according to the invention.
According to a first preferred embodiment according to the invention, within the scope of said implementation, the device is such that the complementary reaction section is connected on the one hand to said distillation zone, at the height of a draw-off level, by a feed means, and connected on the other hand to said distillation zone in proximity to, generally substantially below, said level by a means intended for circulation of the effluent of said complementary reaction section. In said first embodiment, the draw-off level is preferably situated between the feed point of the distillation zone and the top of said distillation zone.
According to a second preferred embodiment according to the invention, within the scope of said implementation, the device is such that the complementary reaction section is connected on the one hand to said distillation-reaction zone, at the height of a draw-off level, by a feed means, and connected on the other hand to said distillation-reaction zone in proximity to, generally substantially below, said level by a means intended for circulation of the effluent of said complementary reaction section. In said second embodiment, the draw-off level is preferably situated between the bottom of the distillation-reaction zone and the bottom of the catalyst bed situated in the lowest part of said distillation-reaction zone.
According to a third preferred embodiment according to the invention, within the scope of said implementation, the device is such that the complementary reaction section is situated at least partly on the means intended for circulation (as reflux) of the effluent from the distillation-reaction zone to the distillation zone, i.e. the means intended for circulation of the effluent from the distillation-reaction zone to, the distillation zone, one end of which is generally situated at the bottom of the distillation-reaction zone, is connected to the complementary reaction section, and the means intended for circulation of the effluent from the complementary reaction section to the distillation zone provides at least partly the reflux of the distillation zone. There is possibly another means for circulating the effluent directly between the bottom of the distillation-reaction zone and the top of the distillation zone, providing at least another part of the reflux.
Generally, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the means for feeding the complementary reaction section preferably comprises at least one temperature control means allowing to adjust the temperature of the effluent flowing into the complementary reaction section, usually in order to obtain the maximum conversion in said complementary reaction section.
Similarly, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the means intended for circulation of the effluent of the complementary reaction section preferably comprises at least one temperature control means allowing to adjust the temperature of the effluent flowing out of the complementary reaction section, usually in order to recover the thermal level of the zone into which the major part of said effluent flows thereafter.
Besides, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the complementary reaction section comprises at least one additional reactant delivery means, usually in order to adjust the conversion in said complementary reaction section.
The invention also relates to a process for preparing at least one tertiary alkyl ether by reaction of at least one aliphatic monoalcohol with at least one olefin, comprising:
a) contacting in a reaction section at least one olefin and at least one aliphatic alcohol, generally in excess,
b) introducing, through at least one circulation means, the major part of the effluent of said reaction section into a distillation-reaction section comprising a distillation zone and at least one distillation-reaction zone, comprising at least one catalyst bed, said distillation-reaction zone being distinct from the distillation zone and providing at least partly, preferably for the most part, most preferably practically entirely, the reflux of the distillation zone,
c) drawing off, at the bottom of the distillation zone, tertiary alkyl ether and at the top of the distillation-reaction zone, an effluent comprising unreacted hydrocarbons and residual aliphatic alcohol.
The process according to the invention is preferably such that the major part of an effluent drawn off at the top of the distillation zone is fed into the distillation-reaction zone and the major part of an effluent that is recovered at the bottom of the distillation-reaction zone is fed to the top of the distillation zone.
The process according to the invention is also preferably such that the reflux of the distillation-reaction zone is provided by drawing off, at the top of the distillation-reaction zone, at least one effluent the major part of which is condensed, part of said condensed effluent being re-introduced at the top of the distillation-reaction zone and the other part of said condensed effluent forming mainly the part drawn off as described at c) above.
A preferred implementation of the process according to the invention is preferably such that said process is characterized in that said distillation-reaction section comprises at least one complementary reaction section, comprising at least one catalyst bed.
Such a preferred implementation comprises three embodiments which are described hereafter, and said embodiments can be combined with each other in order to achieve said preferred implementation of the process according to the invention.
According to a first preferred embodiment according to the invention, within the scope of said preferred implementation, the process is such that the complementary reaction section is supplied with at least part, preferably with the most part of an effluent drawn off at the height of a draw-off level of the distillation zone, the effluent of said complementary reaction section being fed for the most part into said distillation zone in proximity to, generally substantially below said level. In said first embodiment, the effluent is preferably drawn off between the feed point of the distillation zone and the top of said distillation zone.
According to a second preferred embodiment according to the invention, within the scope of said preferred implementation, the process is such that the complementary reaction section is fed with at least part, preferably with the most part of an effluent drawn off at the height of a draw-off level of the distillation-reaction zone, the effluent of said complementary reaction section being fed back into said distillation-reaction zone in proximity to, generally substantially below said level. In said second embodiment, the effluent is preferably drawn off between the bottom of the distillation-reaction zone and the bottom of the catalyst bed situated in the lowest part of said distillation-reaction zone.
According to a third preferred embodiment according to the invention, within the scope of said preferred implementation, the process is such that at least part, preferably the most part of the effluent circulating from the distillation-reaction zone to the distillation zone in order to provide at least partly the reflux of the distillation zone, passes through the complementary reaction section, i.e. at least part, preferably the most part of said effluent is fed into the complementary reaction section, then the major part of the effluent of said complementary reaction section is fed into the distillation zone. Another part of the effluent possibly circulates directly from the distillation-reaction zone to the distillation zone.
Generally, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the temperature of the effluent flowing into the complementary reaction section is preferably controlled, which allows to adjust the temperature of the effluent flowing from the complementary reaction section, usually in order to obtain the maximum conversion in said complementary reaction section.
Similarly, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the temperature of the effluent flowing from the complementary reaction section and flowing into the distillation zone is preferably controlled, which allows to adjust the temperature of the effluent flowing into the complementary reaction section, usually in order to recover the thermal level of the zone into which the most part of said effluent flows thereafter.
Besides, within the scope of said preferred implementation, whatever the embodiment of the device according to the invention, the complementary reaction section is preferably supplied with additional aliphatic alcohol, which usually allows to optimize the ether(s) yield in said complementary reaction section.
Finally, in the etherification process, the presence of the complementary reaction section, when there is one, advantageously allows to control at best two significant parameters which are the temperature and the addition of alcohol to said section, which favours optimization of the ether(s) conversion or yield.